Method of and means for modulation



Feb. 25, 1936. J cH 2,3l,639

METHOD OF AND MEANS FOR MODULATION Filed Feb. 27, 1933 8 Sheets-Sheet 1 m0 (mu/z KNVENTOR- L, FNCH ATTORNEY- Feb. 25, 1936. L, FINCH 2,031,639

METHOD OF AND MEANS FOR MODULATION I Filed Feb. 27, 1933 8 Sheets-Sheet 2 INVENTOR- J.L.F\NCH ATTORNEY- Feb 25, 1936. J, L. FINCH 2,03L639 METHOD OF AND MEANS FOR MODULATION Filed Feb. 27, 1953 B Sheets-Sheet 3 INVENTOR- J.L. INCH BYrRg MM ATTORNEY- Feb, 25', 19%.. HNCH imsms METHOD OF -AND MEANS FOR MODULATION Filed Feb. 27, 1933 8 Sheets-Sheet 4 1040 may/r 32 3 10,40 c/xw/r INVENTOR- J L. FINCH ATTORNE- Feb. 25,1936. J. L. FINCH 2,031,639

'METHOD OF AND MEANS FOR MODULATION Filed Feb. 27, 1933 8 Sheets-Sheet 5 1040 aka/r as Y 32 [0A0 mm/r INVENTOR- J. L. FINCH 'ATTORNEY- Feb 25 1936 J, L FINCH I f2,@31,639

METHOD OF AND MEANS FOR MODULATION Filed Feb. 27, 1935 8 Sheets-Sheet 6 OOQQQQQQQO INVENTOR J- L FINCH ATTOR N EY Feb. 25, 19360 J, FINCH I 2,31 639 METHOD OF AND MEANS FOR MODULATION Filed Feb. 27, 1935 a sheets-sneak 7 OUTPUT k INVENTOR 5: J.L. FINCH A'ho NEY Feb. 25, 1936. J. FINCH 2,031,639

METHOD OF AND MEANS FOR MODULATION Filed Feb. 2'7, 1933 8 Sheets-Sheet 8 70 s I 2 302 \d lilllllllllm lllm INVENTOR J. L. FINCH ATTORNEY Patented Feb. 25, 1936 UNITED STATES PATENT OFFICE METHOD OF AND MEANS FOR MODULATION James Leslie Finch, Rocky Point, N. Y., assig'nor to Radio Corporation of America, a'corporatmn of Delaware This invention relates to a system of modulation and can be applied to a wide variety of uses, such as for the control of a system of power generation or transference in respect to its intensity, phase, frequency, or other properties. The invention is particularly applicable to modulation of high frequency oscillations in any of their characteristics at signal frequency. It can also be applied to the control of light or heat or fiuid streams or of magnetic fields, or to the speed of moving elements or vehicles.

The principle upon which the present invention operates is that of providing a detecting device in the system after the point of change or modulation, which detecting device is responsive to the change or modulation desired. The detecting device is equipped with a control element and is so arranged that its output reacts back to a point earlier in the system so as to produce a degenerative effect. The control element in the detector permits the degenerative effect to go to a definite point which is determined by the control element, but no further than said point. The definite point is adjustable. Thus the system is changed or modulated in accordance with the control element in the detector.

In the prior art it has been the practice to produce modulation by means of some control element and to design the system to given linear response to this control element and to suppress any other factors which tend to produce extraneous modulation. Due to the difficulties encountered the resulting modulation is frequently distorted and different from that desired. My invention makes unnecessary these precautions, which are normally expensive and difiicult to accomplish.

The novel features of my invention have been pointed out with particularity in the claims appended hereto. The nature of my invention and the operation thereof will be best understood from the detailed description thereof, which follows, and therefrom when read in connection with the attached drawings, in which:

Figure 1 shows a radio transmitter including my novel oscillation relaying device and my novel control means which determines the character of the oscillation as being relayed. In this arrangement energy is derived from the output of a high frequency amplifier connected to a modulator, impressed on a modulation frequency amcoupling tubes from the modulation frequency amplifier to an electrode in the modulator stage to control the same.

Figures 2 to 13 inclusive show modifications of the arrangement of Figure 1; in Fig. 2, the energy derived from the output of the amplifier is impressed on an inductance connected to an electrode in the modulation frequency amplifier instead of on a capacity, as in Fig. 1; in Fig. 3, the controlled modulating potentials are applied to the output of the high frequency amplifier to accomplish control modulation in the same stage from which the controlling energy is derived; Fig. 4 is similar in many respects to Fig. 1. In Fig. 4, however, anode modulation is accomplished in the modulator stage rather than screen grid modulation,,as in Fig. 1. In Fig. 5, which is similar in many respects to Fig. 3, the controlled modulating potentials are applied to the control electrodes of the amplifier stage to accomplish therein grid modulation. In Fig. 6, which is similar in many respects to Figs. 1 and 4, the controlled modulating potentials are applied by Way of the coupling tubes to the control grid electrodes in the modulator stage. In Fig. 7, the controlled modulation circuits are similar in many respects to the corresponding circuits in Fig. 1, however, in Fig. '7, anode modulation is accomplished in a single stage which is coupled by Way of a pushpull amplifier to the amplifier stage from which the controlling energy is derived. In Fig. 8, additional coupling tubes are interposed between the controlled modulation frequency amplifier and the modulator stage wherein screen grid modulation is accomplished. In the arrangement of Fig. 9, the first coupling tube between the controlled modulation frequency amplifier and the modulator stage is of the screen grid type. In the modification of Fig. 10, the output of the controlledmodulation frequency amplifier is connected directly to the screen grid electrodes in the modulator stage to accomplish screen grid modulation therein. In the modifications of Figs. 11 and 12, the controlled modulation frequency amplifier is of the screen grid type and the screen grid and control grids are respectively capacitively" and inductively coupled to the output of the amplifier stage. The remaining grid-like electrodes in each of the controlled modulation frequency amplifier tubes are connected to the source of modulated potentials. In Fig. 13, modulation is accomplished in an oscillator of the resonant long-linefrequency controlled type. This circuit in other respects is somewhat similar to the circuit of Fig. 4;.while,

Figures 14 and 15 show applications of the principals of my invention to the control of a magnetic field or lines of flux and to the control of a light ray respectively.

I will describe specific embodiments of my invention as applied to the amplitude modulation of a radio transmitter, the modulation of a magnetic field, and the modulation of a beam of light. It will be understood, however, that the invention is readily applicable to other types of modulation.

Referring to Figure 1 of the drawings, A is the final stage of the transmitter. The final stage A is excited by stage B. Thestage B comprises .a pair of thermionic tubes [8 and l9'having the control grids I8 and I9 connected to the :opposite terminals of a winding :21 the'center point of which may be connected, as shown, to the pole of a biasing source, not shown, at C. .The inductance 2| may be coupled by Way of circuit 20 to any source of high frequency oscillations 15. The oscillations impressed from IS on 2| are repeated and amplified in the tubes 18 and I9 and appear in the inductance 24 connected between the anodes of tubes I8 and [9. The oscillations appearing in '24 are applied to the control grids 32 and 33' of tubes 32 and 33 by way of coupling and blocking condensers 25 and26. Biasing potential for the grids 32' and 33 of tubes 32 and 33 is supplied from C connected to a source, not shown, by way of choking coils 29and 30 respectively. The high frequency oscillations impressed on the control grids of the power amplifier tubes in stage A are repeated and amplified insaid tubesand appear in the inductance 34 connected between their anodes. The amplified oscillations may be supplied from the inductance in any manner to a load circuit. 'For example, the energy may be fed to the load circuit through coupling condensers 35 and 36 in lines 31 and 38 tapped to inductance 34.

l is a three element tube which serves as the detector variably coupled by way of its anode 6 and an element to the final stage A and responsive to the amplitude of the output of said stage. The voltage on control grid 2 is made responsive to the voice currents in microphone 3 by means of transformer 4 and bias battery 5. When the voltage impressed on anode 6, .due to the output of A, is high enough to overcome the effect of the blocking voltage on 2, anode current will flow in tube the direct current component returning through resistor I and the alternating current component through smoothing capacitor Reactor 9 is required to prevent the radio frequency anode potential, transferred to 6 from the final stage of A, from being short-circuited by 8. The control grid IQ of amplifier tube II has a potential impressed on it due to the resistance drop of the current flowing through I. This amplifier tube H is resistance coupled to the control grid 12 of modulator tube 12 by means of resistor I3 and bias battery H. The modulator tube I2 has its anode electrode 12" connected to its cathode by way of resistance l1 and a source of direct current voltagenot shown. The screen grid electrodes S and S of tubes 18 and H! are connected, as shown, to the resistance IT. A change of current intensity flowing in resistance I! causes a change in the potential applied to the screen grids of tubes l8 and 19. .As the current through I! decreases the potential ,on the screen grid electrodes 18 and I9 increases and vice versa. In this manner the tube l2 modulates the screen grids of tubes l8 and IS in the radio frequency amplifier stage B.

The proportions of these circuits are so chosen that when the peak radio frequency potential on 6 exceeds the cut-off voltage as determined by the voltage on 2 by an appreciable amount, the reaction back through the modulator tube l2 will reduce the amplitude of the oscillations supplied by stage B to stage A, and the power output of A until the peak radio frequency potential on 6 just barely exceeds the cut-off voltage. Thus, as the potential on grid 2 is varied in accordance with the voice, the cut-off voltage of l is varied in proportion and the peak radio frequency potential output is automatically adjusted to just exceed this voltage. Thus the output voltage is modulated truly in accordance with the modulating potentials.

Now, if some extraneous modulation is introduced, such as a power hum modulation on the output of radio frequency source I5, or if the gain of stage A or B is varied by reason of alternating current on the filaments, or due to inconstant plate or bias voltages, such modulation will be practically eliminated due to the degeneration introduced by the circuits of this invention. More specifically, such extraneous hum will cause an increase of the potential applied to 6. This increase in potential on 6 will act through amplifier II and modulator 12 to instantly reduce the potential on the screen grids S and S of tubes I8 and I9 and reduce the amplitude of the oscillations supplied thereby to stage A.

It will be noted that the amplifier and modulator, tubes l l and I2, employed in this invention need not have a linear characteristic since any distortion introduced from this cause is of a secondary order.

The filament of the modulator i2 is shown at a negative potential with reference to the filaments of the modulated stage B. This is necessary in order to fully modulate the stage B through the screen grids.

The operation of this invention as applied to a radio transmitter using voice control and amplitude modulation is as follows:

Starting with no modulation, grid 2 will assume a potential at the middle of its operating range. Assume also that momentarily tube I2 is blocked, thus allowing stage B to pass a maximum amount of power on to stage A. Stage A will in turn put out a maximum power and coincidently will induce a maximum radio frequency voltage on 6. This causes a direct current potential to be impressed on 1 of a value much in excess of that required when acting through amplifier H and modulator l2 to decrease the output of B to zero, but when this output has dropped to a value low enough for the voltage on the output of A to have dropped to half value, the voltage on 6 will have dropped to a value just sumcient for the peaks to exceed cut-ofi and thus a stable condition at this voltage is maintained. Now assume the voice causes 2 to drop to the most negative potential of its range. This will momentarily cut off tube I, dropping the voltage on i to zero, which will in turn reduce the current in H and cause the screen grids of B to reach their maximum operating potential. This in turn will increase the gain of B and the output of A will rise to its maximum voltage value. The latter will be just sufilcient to impress a high enough voltage on 6 to rectify a small amount of current and thus to maintain this value. Similarly, the output voltage will follow in inverse proportion any voltage impressed on 2 and thus will follow the voice currents.

It wi1l be understood that the arrangement shown in Figure 1 may be modified in various manners without departing from the scope of the present invention. For example, the anode 6 of tube I may be variably inductively coupled by way of inductance 40 with the inductance 34 in the output circuit of the power stage A, as shown.

in Figure 2. When modified in this manner the choking inductance 9 of Figure 1 may be eliminated since the inductance 49 serves the dual purpose of preventing short circuit of the radiofrequencies and for coupling the tube l to the power stage. The circuit in Figure 2 is, as shown, otherwise substantially the same as the circuit of Figure 1.

The modulation of the oscillations may be accomplished in the stage A and anode modulation may be used as shown in Figure 3. This is accomplished by connecting the anode of tube l2 to the lead supplying charging potentials to the anodes of the tubes 32 and 33 by way of the inductance 34. In this manner the modulating tube l2 and the amplifier tubes 32 and 33 both draw current through the resistance IT. The potential of the resistance I! therefore determines the potential applied to the anodes of the tubes 32 and 33 and consequently determines the amplitude of the oscillations impressed from said anodes to the tank circuit including inductance 34. The circuit of Figure 3 may be the same in other respwts as the circuits of Figures 1 and 2 and, as shown, is otherwise substantially the same as the circuit of Figure 1.

Instead of using screen grid modulation in the 2 stage B, anode or plate modulation may be used as shown in Figure 4. When anode modulation is desired the anode electrodes of tubes l8 and 19 are charged by way of inductance 24 and resistance ll. Here tubes I3, l9 and 12 all draw their anode current through the same resistance l1. Consequently, when the tube I 2 draws a heavy current, due to modulation potentials being applied, the potential at the terminal of I! drops and consequently the potential applied to the anodes of tubes l 8 and I9 falls, in this manner modulating the potentials applied to the anodes of said tubes. The circuit of Figure 4 may be otherwise the same as any of the prior circuits and is shown substantially the same as V 1 the circuit of Figure 1.

Where, for some reason, grid modulation in stage A is desired, the arrangement of Figure 5 may be used. In this arrangement, which may be otherwise the same as the prior arrangements ".and is shown similar to the circuit shown in Figure 1, the modulation potentials appearing on the anode of l2 are supplied by way of the battery 4! and the choking inductances 29 and 30 to the control grid electrodes 32' and 33 of tubes 32 and 33 respectively. The control grids ance H and in this manner the bias applied to the control grid electrodes 32' and 33*.respectively is altered at modulating frequency.

Grid modulation in the stage B, as shown in Figure 6, may be utilized when desired. In this arrangement the modulating potentials appearing at the terminalof the resistance H are impressed by way of battery 42 and inductance 21 to the control grid electrodes I3 and IQ of the tubes I8 and [9 respectively. When control grid modulation is utilized the screen grid electrodes s and s' 'of'tube's l8 and I9 may be maintained at the same constant direct current potential by the resistances 22 and 23 connected to the positive terminal of a direct current source not shown. This circuit may be similar to any of the prior circuits except in this respect.

Where more amplification is desired the amplifier stage B may be preceded by an additional amplifier stage C, as shown in Figure 7. Moreover, the oscillations provided from source 65 may be modulated in this additional stage. This stage may comprise an inductance 49 coupled to the inductance 2!]. Charging potential for the control grid 48 of tube 48 can be supplied, from a source not shown. The high frequency current circuit between the grid 48' and cathode of tube 48 is completed by way of a by-pass condenser 50. The high frequency oscillations repeated and amplified in tube 48 appear on the anode thereof and in the inductance 54. The inductance 54 is tapped, as shown, and one terminal thereof may be connected to the cathode by way of a balancing capacity 53. The anode circuit of the tube 48 may be tuned to the. frequency of the source l5 by the series capacities 5| and 52. The tube 48 may be of any type and is shown as a screen grid tube. The screen grid electrode S is charged by way of a resistance R. connected to the positive terminal d+ of a source of potential, not shown. This stage may be modulated in any manner. For example, anode modulation may be accomplished by connecting a point on the inductance 54 to a terminal of the resistance ll so that the anode electrode of tube 48 draws its current through the resistance ll. Of course, if desired, screen grid modulation may be used. This is accomplished, as shown in Figure 1, by connecting the screen grid electrode of the tube 48 to the terminal of the resistance ll. When screen grid modulation is used the anode electrode of tube 48 may be charged from any direct current source by connecting a point on the winding 54 to said source. The circuit of Figure 7 as shown is otherwise similar to the air cuit of Figure l, but may be similar in other respects to any of the preceding circuits.

Where more amplification of the modulating signal is desired the circuit arrangement of Figure 8 may be used. In this circuit additional tubes 42 and 43 are connected between the amplifier II and the amplifier [2. Each of these tubes increases the amplitude of the modulating potentials. Modulating potentials of increased amplitude are applied, as in Figure 1, to the control grid electrode of tube H. to determine the conductivity of said tube. The anode electrode of tube l2 is charged by way of a resistance l1 and the drop in potential across the resistance ll may be used to modulate the high frequency oscillations in any manner. The circuit otherwise may be the same as any of the circuits in the preceding figures.

' In some cases a different type of amplifier may be used between the tube l and the tube l2, as shown in Figure 9. For example a tube 55 of the indirectly heated cathode type may be utilized. Furthermore, this screen grid tube of the heater type may have its anode connected to the control grid tube of [2 by way of a potentiometer resistance 59 having one terminal connected to the anode of 55 and the other terminal connected to a negative. source of potential. The control grid of i2 may be connected to the movable point on the potentiometer so that the control potential applied to the control grid l2 may be adtube 64.

55 may be charged with positive potential from a source not shown by way of a resistance 58'. Radio frequency oscillations may be. bypassed around said source by a by-pass condenser: 51. This circuit may be otherwise substantially similar to the circuits shown in Figures 1 to '7 inclusive.

Where lower powers are used and the ampli-' tude of the modulating potentials does not need: to be so high, the circuit arrangement of Figure 10 may be-used. In this circuit arrangement the modulating potentials appearing across the resistance I are applied directly to the screen grid 1 electrodes l8 and 19 of tubes l8 and I9 respectively. These varying potentials vary the conductivity of the tubes 18 and H! or alter'theimpedance of said tubesso that the potentials appearing on the anodes of tubes I8 and I9 aremodulated at signal frequency.

The modulation frequency amplifier I may be a triode as shown in the preceding circuits, or may' be of the screen grid type as shown in Figure 11.

When a tube of the screen gridtype, such as; 1 tube 64, is used the anode is connected by way of a charging source 6! to the terminal of the resistance I. The resistance 1 is connected to the control grid H! of amplifier H through av second source 56. The inductance 34 is capacitively coupled to the screen grid electrode 64 of tube 64.

a choke 62 and a source of potential 63, a terminal of which is grounded, as is the cathode of- When the radio frequency voltage induced on the screen grid 64' of 64 has attained the maximum positive value, it is assumed thatthe tube 64 will pass plate current then, and.

then only. This plate current reacts through the succeeding amplifiers ll, l2, etc., as explained before, to prevent the radio frequency voltage appearing in 34 from exceeding a critical value.

This particular critical value changes. with thecontrol grid voltage on the control grid oftube 64. In this way modulation of the oscillations re-- layed in the stages A and B which is truly charac-- teristic of the signal is accomplished. This-tube 66 may be utilized to replace the tube I in any of the prior modifications.

In some cases it may be-desirable to. use a tube of the screen grid type as a control tube and. apply the modulating potentials to the screenv grid and the control potentials to the control grid. In this case a circuit? as shown in Figure- 12 may be used. Here, as in the prior case, the

anode of the tube 64 is supplied with positivepotential by a source 6| and the terminal of resistance I is connected to the control grid l of tube I I through a second source 56. Here, however, the control potentials are applied on the control grid Cg of tube 64, which is maintained at a negative potential with respectv to the cath-- ode by a battery 63. connected to the choking inductance 62. It is noted that the battery here has its terminals reversed with respect to the:

Charging potential for the screen. grid electrode 64 of tube 64 is charged by wayof' justed. The screengrid electrode 55 of thetube- This invention can be applied to any type of transmitter knownin the prior art. For example, a transmitter: comprising an oscillation generator stage G- anda: power amplifier stage D, as connectediinEigure 13, may be utilized. The oscillation generator G. may include a pair of thermionic tubes 66 and 61 having their control electrodes connected by way of. movable taps 89 and 9|] to.- a long line frequency control circuit 65 resonant'to thefrequency it is desired to produce. Such along line frequency control generator has been illustrated in detail in United States application Serial No. 363,660, filed May 16, 1929, and a description thereof, except as given hereinafter, is thought unnecessary. Charging potential for the-control grid electrodes 66' and 61' ofv tubes 66 and 61: respectively is suplied by connecting the electrical center of that portion of the frequency control circuit between the taps 89 and 90-tol ground by way of inductance 85 and resistance 83. The inductance 85 acts as a stopper to the: high frequency oscillations, while the resistance 83 is'shunted by by-pass condenser 86 which forms: a short circuit for any oscillations which get through the inductance 85. The inductance 85 maybeshunted by a resistance 84, the purpose of which will be described later. The anode electrodes of tubes 66 and 61 are connected to a tank circuit including an inductance TI and a tuning capacity 10. The desired feed-back necessary for oscillations in this circuit is attained by theuseof two feed-back condensers 68 and. 59 connected as shown. The oscillations developed in the tubes66 and 61 may be supplied to the following balanced stage D by way of inductance 12 coupled to an inductance TI. The inductance 12 has its terminals connected to the control grids l and 16 of power amplifier tubes 15' and i6, asshown- The electrical center of the inductance i2 is connected by way of a choking inductance 13 to a source of negative potential not shown. The source of negative potential not shown isshunted by by-pass condenser 16. The anodes of tubes 15 and 16 are connected to a secondtank circuit comprising a tuning capacity 8.] and an inductance 34. Charging potential for the anodes of tubes 15 and 16 is supplied by way of a choking inductance 88 and any source of potential not shown. The source of' positive potential not shown may be shunted by by-pass condenser 11 as shown. The circuit may be neutralized as shown by connecting the anode of tube 15. to the control-grid electrode 16' of tube 16 by way of a neutralizing capacity 78-, while the anode of. tube Hi-is connected to the control grid electrode. 15' of tube 15 by way of a neutralizing capacity 19, thus preventing self-oscillations in this stage. The high frequency oscillations relayed and amplified inthe tubes 75 and 16 appear inthe tank circuit and may be supplied from the inductance 34 thereof to any utilization circuit by way of leads 36 and 37, as described more in detail hereinbefore.

The control circuit including the tubes I, H and L2 issubstantially similar to the equivalent elements shown in Figure 1. The anode 6 is coupled by a capacity 8 to the output circuit of tubes 15 and 16. Here, however, the anode l2 of the tube [2 is connected to the positive terminal of a battery 82, the negative terminal of which is connected to the intersection between the resistance 84 and the resistance 83. In this manner variations in potential appearing on the anode I2" of tube l2 are transmitted to the control grid electrodes 66 and 61' of tubes 66 and 61 respectively. As described hereinbefore, plate currents are set up in tube I and react in tubes I I and I 2 to control the output of the transmitter. In this case the tube I2 controls the bias on the master oscillator G of the transmitter when the radio frequency induced on plate is sufiicient to overcome the bias of tube I and cause current to flow. The flow of current through resistor 1 will produce a negative potential on the grid of tube I I, which in turn will produce a bias on the grid I2 of the tubeIZ by virtue of the resistance and battery coupling I3 and I4 respectively. This decrease in bias on the control grid of tube I2 will allow more current toflow through the plate circuit of tube I2, through battery 82 and resistor 83. Change in flow through the resistor 83 produces changes in the potential dropped therein and consequently a change in the potential on the terminals thereof. This change in potential is impressed through resistor 84 and inductance 85 to the long line 65 and thence to the control grids 66 and 61 of the master oscillator tubes 66 and 61. This increase in bias voltage on the control grids oftubes 66 and 61 will decrease the output of the master oscillator, which in turn will decrease the output of the power amplifier. In this manner the output of the power amplifier will be maintained at a value just sufficient to cause current to flow in the plate circuit of tube I, which in turn will be truly proportional to the voltage induced from the source 3 on the grid of tube I.

While I have shown my control circuit as being especially applicable to radio frequency transmitters in connection with the modulation circuits therein, I do not wish to be limited to such circuits only since, obviously, this present invention has a wide application in the electrical and other arts. invention may be applied to the control of or the modulation of the intensity of a magnetic field, as illustrated in Figure 14.

Referring to Figure 14, KM represents a core of magnetic material which has an air gap I02. A magnetic field is induced in this core by the passage of current through winding I06. I have assumed that we desire to modulate the intensity of the magnetic field across the portion marked X. Accordingly, I have shown twoarms of magnetic material connected at this point, between which is placed magnetron I E33. This magnetron has a filament I94 which is heated by a source of voltage Hi8, Surrounding this filament is a cylindrical plate I05. I make use of the well known property of the magnetron to present a variable plate to filament impedance in proportion to variations in the magnetic field in which it is placed. Battery I69 is used to force current through the plate filament circuit of the magnetron and through resistor IIB. Thus the total voltage of see is divided between the plate filament circuit of I03 and resistor H0. It isassumed that the characteristics of I03 are such that the voltage across H9 will be caused to vary in proportion to the strength of the magnetic field through I03.

The intensity of the magnetic field in NH is controlled by the amount of current flowing through winding I66, This current is induced by battery I0? and is controlled by vacuum II'I. Vacuum tube I I? in turn is controlled by vacuum tube li l, which is coupled to it, for purposes of illustration, by means of the resistor I I 5 and bias battery H6. Vacuum tube II4 is in turncontrolled through its grid by the voltage impressed across resistor I 50 and by voltage induced in the For example, the principles of my secondary of transformer H3. The voltage in duced in the secondary of H3 can be controlled as desired, as, for instance, by means of the voice operating through microphone III with battery H2 in the primary circuit of II 3.

If we assume for the moment that no voltage is being induced in the secondary of IE3 then a state of equilibrium will be found in which the magnetic field across X is of a particular value which can be adjusted to any desired value by adjusting the voltage of the various batteries. In case this field is temporarily in excess of this value then the impedance of magnetron I03 will be high. This will result in the voltage across II 0 being low, This in turn will cause tube II 4 to be more conducting, which will make the voltage on the grid of II! more negative. This in turn will increase the impedance of II! and will therefore restrict the current flowing through I06 and reduce the field at X to the value originally assumed. In case the field at X is lower than normal a similar chain of reasoning will show that it will'rise to the normal value.

If we now assume that a voltage is induced in the secondary of I I3 then a state of equilibrium will be attained at a different value of field at X. Following the same line of reasoning as above,

it can be seen that the value of the field X will vary in proportion to the induced voltage in the secondary of H3, which is the condition which was originally desired. It will be noted that this Will be the case in spite of any non-linearity which may exist between the field at X and the current in winding I06 within the limits of range of this apparatus.

The control system of' the present invention can also be used to control or modulate the intensity of a source of light, as illustrated in Figure 15.

In Figure 15 I have shown my invention as applied to the modulation of a source of light as used in television. The source of light I33 is of the glow tube type such as is used in certain types of television apparatus. Its characteristic is such that an increase in current through it results in an increase in light emitted from it. This light casts a bear'non screen I35 through holes in scanning disk I 34 in the well known manner. In my invention I place a photoelectric cell I 32 in such a position relative to I-33 that the light it picks upis proportional to the light which is projected upon the screen I35. I have shown circuits by means of which the intensity of light is controlled by this photoelectric cell I32 to respond to the value required by some controlling element. In this particular illustration battery I28 forces a current through I32 and through resistor IZ'I. The impedance to the passage of this current which I32 offers is assumed to be inversely proportional to the intensity of the light. Accordingly, voltage across resistor I21 will be proportional to the intensity of the light provided the relative values are properly chosen. In my illustration battery I3I forces current through lamp I33 and vacuum tube I30. This current will vary with the voltage which is impressed on the grid of I30. Accordingly, the light emitted by I33 can be controlled by the voltage on the grid of I30 although a proportional relationship will not necessarily exist.

The voltage on the grid of I30 is determined partly by the voltage across I21 and partly by the voltage induced in secondary winding I29 of a transformer with primary winding I26. If

for the moment we assume that no voltage is induced in I29 then a state of equilibrium will be obtained with aparticular value .of light as determined by'the :various constants of the circuit. Should this light be greater than this value the impedance of I32 will drop below normal and the voltage across 121 will .become morenegative than normal and this negative voltage is impressed on the grid of I30, and when'the latter is more negative than normal the plate impedance of I30 will be higher than normal. This decreases the current which can fiow through lamp I33 until the normal condition is attained.

If we now assume that currents are passed through primary winding I26 so as to induce voltages in secondary winding I29, it will be seen that new values of light will be emitted by lamp I33 in proportion to the voltages induced in I29. For purposes of illustration I have shown two methods of controlling the induced voltage .in I29. In one case I have shown microphone I24 and battery I25 connected inseries with I26. In this case the voice at the microphone would control the intensity of the light as projected on screen I35. In the other case it is assumed that I24 and I25 are disconnected and in its place is connected the radio receiving circuit .numbered I I8 to I23. In this case asignal is assumed to be impressed on antenna I2I, causing a voltage to be set upacrossresistor I22. This is coupled to the grid of vacuum tube I I8 through grid leak H9 and by-pass capacitor I20. Tube II8 acts as a detector being shunted by 'by-ipass capacitor I23. Thus thecurrents passed through the primary of I26 and the plate circuits of II9 will be proportional to the envelope of the radio frequency signal which is impressed on I2I. Thus, as explained 'above, the intensity of the light on screen I35 will vary in proportion .to the envelope of the :radio frequency :signal zimpressed on I'2'I.

While .I :have shown the .present invention as being applied :to I the :control of the :amplitude of oscillations, the control of 'modulation'of oscillationsythe control of :a magnetic circuit,:andrthe control of the intensity :of :a beam .of light, :it will be :understood that :I do not intend to be limited by such showingsince, obviously, the present invention is 'of :much wider scope. For example, the method and %means of the present invention :may be utilized to control energy in practically anytform. TBy energy .I mean kinetic and. potentialenergy, that is, energy in'anyform.

In the "claims the-words level or value of energy :havebeensused to :describe what may be controlled by my control method and "means of the presentinvention. By level of'energy I mean the maintenance 'in :a predetermined state 'of energy of any type'known, either potential energy or kinetic energy. Where the claims speak of controlling the value of energy they include the maintenance of kinetic or potential energy in any state, constant or otherwise-as long as it is a predetermined state.

The control method andmeans for carrying out the scheme of the present invention is applicable to practically all of the arts, electrical, mechanical and chemical. In particular, the method .of and means for controlling values or levels of energies of the present invention is applicable to the elements-enumerated below.

1. The levelof fiuidina reservoir.

2. The velocity of a'fluid stream.

3. The velocity of a moving object.

4. The voltage .of an electrical power generator.

5. The intensity of .a.magneti,c field.

6. The degree ofheat inanoven.

7. The frequency of an electrical oscillation generator.

8. The deviation in phaseof :an electrical oscillation generator.

9. The current delivered by any part-of a radio signalling system.

Having thus described my invention and the operation thereof, what -I claim is:

l. A signalling system comprising, a source of high frequency oscillations, a thermionic tube having its input electrodes connected to said source, a power amplifier having its input elec trodes coupled to the output electrodes of said first named tube, a source of modulating potentials, an amplifier comprising .athermionic tube having its control gridelectrode-coupled to said source of modulating potentials and its output electrodes coupled to an electrode in said first I named tube,a coupling between the output electrodes of said power amplifier and an electrode in said second named amplifier-and means for biasing'the control grid el'ectrode'of said second named amplifier tube to such a value-that peaks only of the energy transferred by Way of said last named'coupling from the poweramplifier to the electrode in the second named-amplifier affeet the operation thereof.

2. A signalling system comprising, a source :of high frequency oscillations, a thermionic tube of the screen grid typehavingits input electrodes coupled to said source 'of high frequency oscillations, a first amplifier tube having its input electrodes coupled to the output electrodes of said screen grid tube, a source of modulating potentials, a second amplifier tube 'having its input electrodes coupled to said source of modulating potentials and its-output electrodes coupled to the screen grid electrodein said first named tube, a-coupling between the output electrodes of said first named amplifier and an electrode in said second named amplifier tube and means for biasing the control grid of saidsecond named amplifier tube to such a value that peaks only of the energy transferred byway of said last named coupling from the first nam'ed amplifier to the electrode in the "second named amplifier affect the operation thereof.

3. A signalling system comprising, a thermionic tube having its input electrodes coupled to a source of high frequency oscillations, a first amplifier having its input electrodes'coupled to the output electrodes of said first named tube, a source of modulating potentials, a second amplifier comprising a thermionic tube having its input electrodes coupled to said source of modulating potentials and its output electrodes coupled to the output electrode in said first named tube, a coupling between the output electrodes in said first amplifier and an electrode in said second named amplifier tube and means for biasing the control grid of said second named amplifier tube to such a value that peaks only of the energy transferred by way of said last named coupling from the first named amplifier to the electrode in the second named amplifier affect the operation thereof.

4. A signalling system comprising, a thermionic tube having its input electrodes coupled to a source of high frequency oscillations, a first amplifier having its input electrodes coupled to the output electrodes of said first named tube,

a source of modulating potentials, a second amplifier comprising a thermionic tube having its input electrodes coupled to said source of modulating potentials and its output electrodes coupled to the input electrodes in said first named tube, a coupling between said first amplifier and an electrode in said second named amplifier tube, and means for biasing the control grid of said second named amplifier tube to such a value that peaks only of the energy transferred by way of said last named coupling from the first named amplifier to the electrode in the second named amplifier affect the operation thereof.

5. The combination of a high frequency oscillation repeater, of a source of modulating potentials, a transfer circuit including the impedance of a thermionic tube coupling said source of modulating potentials to said high frequency oscillation repeater to modulate the oscillations therein, said tube having a control electrode means for regulating the degree of modulation impressed by said source of modulating potentials on said high frequency oscillations, including a second circuit coupling said high frequency oscillation repeater to an electrode in said tube in said transfer circuit to impress peak radio frequency potentials on said electrode to determine the impedance of the latter in accordance with peak amplitude values of the oscillations in said high frequency source, and a source of direct current potential connected with the control electrode of said tube to bias the same to cut off at a point exceeded only by the peak radio frequency potentials impressed on said electrode.

6. The combination of a system responsive to high frequency oscillations, including an output circuit, of a source of modulating potentials, a relay circuit coupling said source of modulating potentials with said system responsive to high frequency oscillations for modulating any high frequency oscillations therein, a thermionic tube having an anode and cathode and control grid, a circuit connecting the anode to cathode impedance of said tube in shunt to said relay circuit, means for regulating the degree of modulation impressed by said modulating potential source by way of said relay circuit on the high frequency oscillation including a coupling between said output system of said circuit responsive to high frequency oscillations and an electrode in said tube in said relay circuit, and a source of direct current potential connected with the control electrode in said tube to bias the same to cut off at a point excited only by the peak radio frequency potentials impressed on said electrode.

trode in said amplifier tube to impress thereon peak radio frequency potentials from said amplifying device, and means in said amplifier tube input circuit to bias the input electrode of said tube to a value such that the cutofi point of said tube is slightly under the peak radio frequency potentials transferred to an electrode therein from said amplifying device, and means for varying said cutoff point at signal frequency, including a coupling between the input circuit of said amplifier tube and said source of modulating potentials.

8. A system for linearly modulating high frequency oscillations from a high frequency source in accordance with signals from a signal source comprising, a thermionic tube having input and output electrodes, means coupling the input electrodes of said tube to said source of high frequency oscillations, a power amplifier tube hav ing its input electrodes coupled to the output electrodes of said tube, an additional thermionic amplifier tube having a control grid electrode connected in an input circuit and an anode connected in an output circuit, a source of potential connected between the control grid and cathode of said additional amplifier tube to bias the control grid of said additional amplifier tube negative with respect to the cathode of said additional amplifier tube, a coupling between the anode of said additional amplifier tube and the output electrodes of said power amplifier tube, a coupling tube connected with the output circuit of said additional amplifier tube, a circuit coupling the output of said coupling tube to an electrode in said first named thermionic tube, and a circuit coupling said source of modulating potentials to the input circuit of said additional amplifier tube.

9. In a system for linearly modulating high frequency oscillations in accordance with signal po tentials, a thermionic modulator tube having input electrodes connected in an alternating current circuit which may be energized by said high frequency oscillations to be modulated, said tube also having output electrodes, at thermionic amplifier tube having input electrodes coupled to the output electrodes of said modulator tube, said amplifier tube also having output electrodes coupled to an alternating current circuit, a second thermionic amplifier tube having input and output electrodes, a circuit coupled between the in put electrodes of said second named amplifier, said last named circuit being adapted to be energized by the signal potentials, a coupling between the anode electrode of said second named amplifier tube and the alternating current circuit coupled to the output electrodes of said first named amplifier tube, an impedance connected between the output electrodes of said second named amplifier, a plurality of thermionic coupling tubes connected in cascade, a circuit coupling the input electrodes of the first of said coupling tubes to said impedance, and a circuit coupling the output electrodes of the last of said coupling tubes to an electrode in said modulator tube.

10. A system as recited in claim 9 in which said modulator tube is of the screen grid type and in which the output electrodes of the last of said coupling tubes is coupled to the screen grid electrode in said modulator tube.

11. A system as recited in claim 9 in which the output electrodes of the last of said coupling tubes is coupled to the input electrodes in said modulator tube.

12. A system as recited in claim 9 in which the output electrodes of the last of said coupling tubes is coupled to the output electrodes in said modulator tube.

13. In a system for linearly modulating high frequency oscillations in accordance with signal potentials, a thermionic modulator tube having input electrodes connected in an alternating current circuit which may be energized by said high frequency oscillations to be modulated, said tube also having output electrodes, a thermionic amplifier tube having input electrodes coupled to the output electrodes of said first named tube and output electrodes coupled to an alternating current circuit, a second thermionic amplifier tube having input and output electrodes, a circuit coupled between the input electrodes of said second named amplifier tube, said last named circuit being adapted to be energized by the signal potentials, a capacity coupling between the anode electrode of said second named amplifier tube and the alternating current circuit coupled to the output electrodes of said first named amplifier tube, a resistance and a capacity connected between the output electrodes of said second named amplifier, and a circuit coupling said resistance and capacity to an electrode in said modulator tube.

14. A system as recited in claim 13 in which said modulator tube is of the screen grid type and in which said last named electrode is the screen grid electrode in said modulator tube.

15. A system as recited in claim 13 in which said lastnamed electrode is one of said input electrodes in said modulation tube.

16. A system as recited in claim 13 in which said last named electrode is one of the output electrodes in said modulator tube.

1'7. In a signaling system for linearly modulating high frequency modulations in accordance with signal potentials, a pair of thermionic modulator tubes each having a control electrode and an anode electrode, an alternating current circuit connected between said control electrodes, said circuit being adapted to be energized by high frequency oscillations to be modulated, a pair of thermionic amplifier tubes each having input and output electrodes, symmetrical circuits connecting the input electrodes of said second named pair of tubes to the anode electrodes of said first named pair of tubes, an alternating current circuit connected between the anode electrodes of said second named'pair of tubes, a modulation frequency amplifier having an input circuit adapted to be energized by modulating frequency potentials, said modulation frequency amplifier having output electrodes connected in a circuit including resistance and capacity, a coupling between an electrode in said modulation frequency amplifier and the alternating current circuit connected between the anode electrodes of said second named pair of tubes, a thermionic coupling tube having its input electrodes coupled to said circuit including capacity and resistance, a second thermionic coupling tube having its input electrodes coupled to the output electrodes of said first named coupling tube, and a circuit coupling the output electrodes of said last named coupling tube to like electrodes in said first named pair of tubes.

18. A system as recited in claim 17 in which said modulator tubes are of the screen grid type and in which said last named like electrodes are the screen grid electrodes of the modulator tubes.

19. A system as recited in claim 17 in which said last named like electrodes are the anode electrodes of said modulator tubes.

20. A system as recited in claim 1'7 in which said last named like electrodes are the control electrodes of said modulator tubes.

21. In a signalling system, a carrier wave amplifier tube having a control grid, an anode, and a cathode, a circuit applying waves of carrier frequency to the control grid and cathode of said tube, an alternating current output circuit connected with the anode of said tube, means for controlling the gain of said tube when energy in said output circuit exceeds a predetermined peak value, and regulating means connected with said last named means for regulating at signal frequency the peak value at which said means hecomes effective to control the gain of said tube.

22. In a signalling system, a carrier wave amplifier tube having a control grid, an anode, and a cathode, a circuit applying waves of carrier frequency to be amplified to the control grid and cathode of said tube, an alternating current circuit connected between the anode and cathode of said tube, means for lowering the gain of said tube when the energy in said alternating current circuit exceeds a predetermined peak value, and a signalling device connected with said means for controlling the peak value at which said means becomes effective to lower the gain of said tube.

23. In a signalling system, a carrier wave amplifying tube having a control grid, and anode, and a cathode, means for applying waves of carrier frequency to the control grid and cathode of said tube, an alternating current circuit connected with the anode and cathode of said tube, means coupled to said alternating current circuit and to an electrode in said tube for lowering the gain of said tube when said energy in said alternating current circuit exceeds predetermined peak values, means connected with said first named means for regulating the point at which said peak values become effective, and signalling means connected with said second named means for controlling said second named means at signal frequency.

24. In a signalling system, a carrier wave amplifier tube having a control grid, an anode, and a cathode, a circuit for applying waves of carrier frequency to said control grid and cathode, an alternating current circuit connected with the anode and cathode of said tube, means actuated by energy in saidlast circuit for lowering the gain of said tube when energy in said alternating current circuit exceeds predetermined peak values, and control means connected with said last named means and with a source of signal potential to be energized thereby for controlling the value at which said peak values become effective to lower the gain of said tube.

25. In a signalling system, a carrier wave amplifier tube having a control grid and a cathode energized by carrier wave oscillations, said tube having an anode connected in an alternating current output circuit, a discharge tube having an electrode connected with an electrode in said amplifier tube for lowering the gain of said amplifier tube when alternating current energy in said output circuit exceeds a predetermined peak value, a coupling between an electrode in said discharge tube and said alternating current output circuit for controlling the operation of said discharge tube by energy from said output circuit, and additional means for controlling the operation of said discharge tube at signal frequency.

26. In a signalling system, a carrier wave amplifier tube having a control grid and a cathode energized by carrier wave oscillations, said tube having an anode connected in an alternating current output circuit, a multi-electrode discharge tube having an electrode connected with an electrode in said first tube for lowering the gain thereof when alternating current energy in said output circuit exceeds a predetermined peak value, a coupling between an electrode in said discharge tube and said alternating current output circuit for controlling the operation of said discharge tube by energy from said output circuit, a source of modulating potentials, and a circuit connecting said source of modulating potentials to an electrode in said discharge tube.

27. In a signalling system, a discharge tube having an anode, a control grid, and a cathode, alternating current circuits connected with said control grid and. cathode and with said anode and 10 cathode, a multi-electrode discharge device, a 

